The algal hepatoxoxin okadaic acid is a substrate for human cytochromes CYP3A4 and CYP3A5

Toxicon. Feb-Mar 2010;55(2-3):325-32. doi: 10.1016/j.toxicon.2009.08.007. Epub 2009 Aug 20.

Abstract

The hepatotoxin okadaic acid (OA) was incubated with nine human recombinant cytochrome P450s (1A1, 1A2, 2C8, 2C9, 2C19, 2D6, 2E1, 3A4 and 3A5). Both CYP3A4 and CYP3A5 converted OA to a mixture of the same four metabolites, but incubation with CYP3A4 resulted in higher levels of conversion. Michaelis-Menten parameters, K(m) (73.4 microM) and V(max) (7.23 nmol of metabolitesnmol(-1)min(-1)) for CYP3A4 were calculated by analyzing double-reciprocal plots. LC-MS(n) analysis and chemical interconversion indicate that metabolites 2 and 3 are the 11S-hydroxy and 11R-hydroxy okadaic acid respectively, while metabolite 4 is 11-oxo okadaic acid. LC-MS(n) analysis of metabolite 1 shows a molecular ion which corresponds to an addition of 16 amu to OA, also suggesting hydroxylation, but the specific site has not been identified. The same four metabolites were produced upon incubation of okadaic acid with pooled human liver microsomes. This transformation could be completely inhibited with ketokonazole, and inhibitor of the CYP3A family of enzymes. The metabolites were determined to be only slightly less potent inhibitors of serine threonine protein phosphatase 2A (PP2A) when compared to OA. As PP2A is the principle molecular target for OA, these oxidative transformations may not effectively detoxify OA.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Biotransformation
  • Chemical and Drug Induced Liver Injury / enzymology*
  • Chromatography, High Pressure Liquid
  • Chromatography, Ion Exchange
  • Cytochrome P-450 CYP3A / metabolism*
  • Cytochrome P-450 CYP3A Inhibitors
  • Enzyme Inhibitors / metabolism*
  • Enzyme Inhibitors / pharmacology
  • Humans
  • In Vitro Techniques
  • Kinetics
  • Liver / enzymology
  • Mass Spectrometry
  • Microsomes, Liver / enzymology
  • Okadaic Acid / metabolism*
  • Okadaic Acid / pharmacology
  • Oxidation-Reduction
  • Protein Phosphatase 2 / antagonists & inhibitors
  • Recombinant Proteins / metabolism
  • Spectrometry, Mass, Electrospray Ionization
  • Xenobiotics / metabolism

Substances

  • Cytochrome P-450 CYP3A Inhibitors
  • Enzyme Inhibitors
  • Recombinant Proteins
  • Xenobiotics
  • Okadaic Acid
  • CYP3A5 protein, human
  • Cytochrome P-450 CYP3A
  • CYP3A4 protein, human
  • Protein Phosphatase 2